Proteinaceous products obtained from seed materials have been extensively used as partial replacement or extender for proteins derived from animal, marine and poultry sources. Defatted proteinaceous materials are conventionally manufactured by extracting lipids and oils from full-fat seed meals or flakes. Protein concentrates are manufactured by extracting the water-soluble or aqueous-alcohol soluble constituents from defatted seed materials. Protein isolates are obtained by isolating the vegetable protein from the non-protein constituents.
Defatted vegetable proteinaceous materials are commonly referred to by the art as vegetable protein products (e.g. Section 102.75, Proposed Rules, Federal Register, July 14, 1978, Part III) with the word "vegetable" being often replaced to identify the seed protein source (e.g. soy protein products). Vegetable protein products containing less than 65% protein are referred to as flour, those containing 65% or more protein by weight to less than 90% seed protein by weight are classified as protein concentrates, and isolates as containing 90% by weight protein or higher.
Indigenous seed constituents adversely affect flavor, odor, flatulent and digestive characteristics of the vegetable protein products. Protein denaturization manufacturing conditions (e.g. heat, alcohol extraction) are customarily used to eliminate these indigenous constituents. Protein denaturization substantially reduces solubility of the vegetable protein.
Vegetable protein products are susceptible to substantial chemical and physical alteration by what may appear to be only minor processing changes. An infinite number of different vegetable protein products may be prepared by simply altering the preparatory processing conditions. The vegetable protein readily reacts or complexes with itself or other constituents indigenous to the seed material as well as processing additives or process conditions which are conventionally used during the vegetable protein product manufacture. The implementation of certain processing changes to correct a specific functional defect often adversely affects one or more equally important functional attributes of the vegetable protein product.
The colloidal or water-soluble vegetable protein concentration (i.e. by weight water-soluble protein) is an important factor in many food recipes (e.g. comminuted meats, diary products, bakery, etc.). Analytically, the water-soluble protein concentration can be ascertained by the nitrogen solubility index (NSI) or protein-in-solution (PIS) tests as shown in Example I. Although the prior art abounds with divergent processing conditions which may be used to correct flavor, odor, digestibility, etc. deficiencies, little progress has been made towards improving the NSI of vegetable protein products. The proposed NSI improvements have been either expensive or impractical in the manufacture of a low-cost vegetable protein product. The problem of achieving a high NSI value becomes particularly acute when an unhydrolyzed, unfractionated protein concentrate or isolate is the desired end-product.
Crushing and homogenization techniques have been used to manufacture vegetable protein products. These techniques are most frequently used in protein isolate production. In the isolate manufcture, the protein is typically extracted with either alkali or acid and then precipitated from solution by isoelectric pH adjustment. The extraction process may cause limited protein hydrolysis and protein fractionation occurs as a result of the isoelectric precipitation thereof.
In U.S. Pat. No. 3,402,165 a high purity vegetable protein product is prepared by finely mashing soybean meal at a pH 3-7 (preferably at its isolectric point) and screening the mash to separate a non-fibrous fraction from a fiber. The fibrous portion, which contains a small amount of occluded protein, is passed through a device at a relatively low temperature to break down the fiberous material by means of supersonic oscillations without destroying the fiber structure per se. After washing with water, the purified fibers are recovered and the proteins removed from the purified fiber is combined with the main protein fraction obtained as a result of the screening step.
High-viscosity vegetable protein concentrates are reportedly prepared in U.S. Pat. No. 3,723,407 by Miller et al. by subjecting a defatted soy flour slurry at the protein isoelectric point (@ pH 3.5-5.5, 4.degree.-38.degree. C. and 10% d.s.) to centrifugation and differential pressures while passing the slurry through a shearing orifice under momentary pressure build-up and sudden pressure release (reportedly disrupts the natural cell structure of the protein), separating the solubles from insolubles (fiber and protein), resuspending the insolubles (@ pH 6.5-8.0 and 40.degree.-80.degree. C.) and spray-drying the resultant protein concentrate.
A patent by Egger et al. (U.S. Pat. No. 3,849,391) discloses a continuous process for producing a vegetable protein product (reportedly low in trypsin inhibitors and undenatured protein) by jet-cooking a defatted soy flour slurry at a pH other than its isoelectric point. In U.S. Pat. No. 4,018,755 vegetable seed protein are extracted from defatted soy flour by sonicating a low solids, alkali flour slurry; centrifuging the sonicate and recovering a water-soluble protein therefrom. U.S. Pat. No. 3,728,327 reportedly produces protein isolates by homogenizing a low solids soy flour slurry, centrifuging the homogenized slurry and recovering the protein isolate from the supernatant by reverse osmosis.